Extrusion die

ABSTRACT

Extrusion die for extruding plastic netting and consisting of inner and outer die members rotatable relative to each other and having surfaces defining die orifices wherein the surfaces of the die members having the die orifices are cylindrical and not in contact with each other, the mechanical thrust in the direction of the axis of the die being borne by frustoconical portions of the inner and outer die members.

United States Patent References Cited UNITED STATES PATENTS 2,919,467 l/1960 Mercer 18/14 X 3,051,989 9/1962 Mercer... 18/14 X 3,070,840 1/1963 Mercer... 18/12 3,193,604 7/1965 Mercer 18/14 X Primary Examiner-James M. Meister Att0rney--Hoge T. Sutherland ABSTRACT: Extrusion die for extruding plastic netting and consisting of inner and outer die members rotatable relative to each other and having surfaces defining die orifices wherein the surfaces of the die members having the die orifices are cylindrical and not in contact with each other, the mechanical thrust in the direction of the axis of the die being borne by frustoconical portions of the inner and outer die members.

PAIENTEDSEPMM 3504.055

same or 2 FIG-3 m m Q g WMFX'H mvsmoxs JOHN A. IcHARDY THOIAS UROUHART BY W ATTORNEY EXTRUSION DIE This invention relates to dies used in the process of extruding plastic netting or other reticulated structure. Such dies are designed to be concentric and rotated in opposite directions. The existence of slots in the dies result in the extrusion of plastic netting having a substantially uniform structure and having a continuous tubular shape. 7

The netting is disclosed in Canadian Pat. No. 652,!96 issued on Nov. 13, 1962 to Frank B. Mercer and the dies are shown in Canadian Pat. No. 642,906 issued on June 12, 1962 to Frank B. Mercer.

The known dies consist of two portions, an inner and outer. The inner has slots cut in its outer circumferential surface. Its shape is frustoconical and the surface has an inclination of from 4 to from true face. The larger diameter of the conical section is the terminating edge of the die lip. The outer portion of the die also has slots cut in its inner surface which is at an angle corresponding to that of the inner portion of the die.

The die then consists of the inner and outer portions suitably mated so that their slotted surfaces are in contact. As the two portions of the die are contrarotated, the various slots pass in and out of register with each other. Molten plastic streams flowing through the slots unite as the slots are in register to form junctions, and separate to form strands as the slots pass out of register.

It has been held to be essential for the two cooperating conical surfaces of the two portions of the die to be drawn tight in order to avoid flashing between the plastic strands. The two slotted surfaces rotating in opposite directions under pressure causes excessive wear of the die lips. The dies can no longer be used following the occurrence of wear and must be restored or replaced.

It is an object of the present invention to provide a die assembly suitable for the manufacture of plastic netting which is more durable and simpler to maintain.

The invention consists of a die structure including inner and outer portions each having slotted cooperating extrusion surfaces which are essentially parallel throughout their cross section, and cooperating tapered thrust surfaces removed from the extrusion surfaces.

The invention is illustrated in one embodiment by referring to the attached drawings, in which:

FIG. 1 is a sectional elevation of the die assembly showing the inner and outer portions thereof assembled for use.

FIG. 2 is a cross section of the assembly taken along the line 22 in FIG. 1 showing the thrust surfaces.

FIG. 3 is a perspective view of the inner portion of the die assembly illustrating the thrust surface and the die orifice surface.

FIG. 4 is an inverted plan view of the die assembly illustrating the relative position of the die orifices.

In' the drawings, 1 is the inner portion of the die assembly, provided with mounting holes 2 and 3 through which may be fitted bolts or other suitable means to connect the inner portion to the appropriate part of an extruder. The outer portion 4 is similarly provided with mounting holes 5 and 6. The inner and outer portions are shaped so as to provide an annular feed ring shown at 7 through which the molten plastic flows on its way to the extrusion interface 8 between the two die portions. The thrust surfaces are shown together at 9 and another annular feed ring is seen at 10. In FIG. 2 the slots 11 are shown in the annular thrust surface of die portion 1 which enable molten plastic to flow from the feed ring 10 to feed ring 7. The slots 11 are seen again in FIG. 3 wherein 12 is the thrust sur face of the inner portion 1. In FIG. 4 may be seen the slots 13 and 14 in the die portions 1 and 4 respectively.

In operation, molten plastic from a suitable source flows into the annular feed ring 10, passes through the slots 1 l to the annular feed ring 7 and is extruded through the slotted sections 13 and 14. The dies being contrarotated at the time, the alternate meeting and separation of the slots produces a mesh or nettin in a continuous fashion.

It will e evident that the two portions of the die are not In contact as closely in the extrusion sections as they are in the known designs. In fact, as best seen in FIGS. 1 and 4, the vertically disposed, slotted extrusion surfaces of the inner and outer die portions are not in actual contact at all. Surprisingly, the extruded netting does not exhibit flashing, largely due, it is thought, to a combination of the pressure drop as the molten plastic passes through the restricted area and the slots pass in and out of register and the shear factor of the molten plastic.

The thrust inherent in the structure is taken up by the frustoconical surfaces which may be constructed of a suitable material, normally a metal alloy such as steel, which has a greater hardness and thus resistance to wear than the more delicate extrusion sections. Since the latter do not contact the other, wear becomes negligible. In the event that the thrust surfaces become unduly worn, they or one of them may be restored or replaced independently of the extrusion sections.

We claim:

1. A die assembly for extruding plastic netting consisting of inner and outer die portions rotatable relative to each other and each having slotted cooperating extrusion surfaces defining a circumferentially extending series of extrusion die orifices wherein the die orifices in each set are opposite directions, the netting is formed, the improvement wherein the slotted cooperating extrusion surfaces of the inner and outer die portions defining the die orifices are vertically disposed and are essentially parallel throughout their cross section and are not in contact, and the mechanical thrust in the direction of the axis of the die is borne by separate cooperating tapered frustoconical thrust surfaces of the inner and outer die portions removed from the extrusion surfaces thereof. 

1. A die assembly for extruding plastic netting consisting of inner and outer die portions rotatable relative to each other and each having slotted cooperating extrusion surfaces defining a circumferentially extending series of extrusion die orifices wherein the die orifices in each set are opposite directions, the netting is formed, the improvement wherein the slotted cooperating extrusion surfaces of the inner and outer die portions defining the die orifices are vertically disposed and are essentially parallel throughout their cross section and are not in contact, and the mechanical thrust in the direction of the axis of the die is borne by separate cooperating tapered frustoconical thrust surfaces of the inner and outer die portions removed from the extrusion surfaces thereof. 